I have high blood pressure and so I want to practice Samatha meditation because that focuses more on relaxation. Trouble is, I'm not sure what it entails.

I've been doing Vipassana (insight) every day for the last four months, but I am new to all of this, and when I looked into Samatha (calm), I couldn't see any differences in technique. Both say to focus on the breath.

Could someone please point me in the direction of a concise explanation on how to practice Samatha so I can relax a bit?

Beyond just reading the sections on concentration in MCTB (e.g. here and here), many practitioners have gotten a lot out of working with the book The Mind Illuminated to develop samatha and vipassanna in tandem. It may also be worth keeping in mind that whatever technique you're using will inevitably stir up some complex emotions. It's very natural at times to feel like meditation is making anxiety worse rather than better, at least in the short run.

Beyond just reading the sections on concentration in MCTB (e.g. here and here), many practitioners have gotten a lot out of working with the book The Mind Illuminated to develop samatha and vipassanna in tandem. It may also be worth keeping in mind that whatever technique you're using will inevitably stir up some complex emotions. It's very natural at times to feel like meditation is making anxiety worse rather than better, at least in the short run.

Thank you JP

Your last part about meditation sometimes making anxiety worse, in the beginning, sounds familiar to me. I have a blood pressure reading unit, and for the last three times I've meditated (30 mins), it has reached 148 / 99 (and sometimes higher). Funny thing is that I don't feel stressed when this happens. Later, my BP drops to almost normal. I've not had the BP unit long so I'll continue to monitor this.

In particular, the 10-Points Practice may be the best I've found for locating and releasing tension (fwiw I find Earth Breathing less productive in that regard). It's taught lying down, legs elevated, knees together, with a cushion/pillow under the head and a yoga strap/belt cinched across the lower thigh creating a trianglar base in the lower legs. I find that posture very comfortable.

It might seem obvious, but it can be very helpful to do a quick "tension scan" every once in a while during your day, even off the cushion. Just let your attention move lightly around the body (or a wider focus on the whole body) and any place you feel muscular tension, let it go. Do this a few times a day, and also any time you notice muscular tension developing. Eventually it becomes a habit (and you become less likely to tense up in the first place), which can really help with anxiety and stress. You'll also learn a few things about the relationship between tension and anxiety.

Welcome! I would also make sure you have a game plan for dealing with intense emotions as they come up. A therapist/friend/health care provider can help you talk through things. Always good to have a strong base of support to work from!

Also thinking of the breath (or whatever else you're focusing on) as a lifeline that always tethers you to safety might be helpful.